Saturday, July 18, 2009

Your background Is Blurry For A Reason.

In my previous blogs I discussed ISO, and shutter speed. This week, I will explain Aperture and how to apply this concept to your photography.

Just as the human eye can change the size of it’s pupil in different lighting, your camera can change it’s own pupil. Inside many nicer pro-soumer, and every SLR camera (Lens) is an adjustable pupil. The sizes of the opening, allowing light to enter the camera when the shutter is open is known as Aperture. Aperture is adjusted to alter the amount of light allowed to enter the camera. Just like shutter speed, and ISO, Aperture can be used to obtain a perfectly exposed image. But, unique to this adjustment, Aperture also impacts the depth of field of the image you are shooting.

How to apply Aperture?
Aperture is referred to as “F-Stop”. The lower the F-Stop number, the wider the Aperture size, the higher the “F-Stop” number, the smaller the aperture size, or opening. As mentioned above, Aperture has two effects. The first and more obvious, is exposure. Using a wide open aperture in low light will help you maintain a lower ISO, and faster shutter speed. In bright conditions, you can also open the aperture to use extremely fast shutter speeds to capture fast action shots with minimal of blur. (Note: Using the lowest F-Stop is referred to as “Wide open”).

So why would you ever want to increase F-Stop?
The answer to this involves Depth of field. Depth of field (DOF) is the portion of a scene that appears sharp over the plane of distance. While a larger aperture (Low F-Stop) will allow more light to expose the image, it will reduce the Depth of field of the image you are capturing. A Higher F-Stop (smaller Aperture), reduces the volume of light, but increases the dept of field allowing more of the foreground and background to appear sharp.

A landscape image would benefit more if the entire image appears sharp no matter the distance from the lens. For this reason a high F-Stop is required. Many photographers use a tripod when shooting a landscape even though daylight usually permits a relatively fast shutter. Because, they are using a very high F-Stop, and low ISO, a longer shutter is required, even in daylight.
(This plant is only a few inches tall yet the top of the plant is out of focus while the bottom is in perfect focus. The low depth of field is caused by the Aperture (F-Stop) being set very low, or "Wide Open")


In many close-up images, the photographer prefers that the subject be in perfect focus while the background is blurry. This helps prevent the background from distracting the viewers, and keeps attention on the subject. To achieve this, a low aperture is required. Since a low F-Stop, also permits a faster shutter, many nature photographs are shot in this fashion.

Just as in ISO, and shutter speed, many cameras have an “Aperture mode” that allows you to set the Aperture manually, while the camera will adjust the ISO and shutter speed automatically to obtain a well exposed image. Just turn that dial to the “A” to select this mode.

About the images shown: All the these images were shot close up "Wide Open". The plants were only a few inches in size. Notice that even though there is small difference in distance, in some cases approximately only an inch, portions of the image are out of focus. All images were shot with relatively fast shutter, in day light with an ISO of 80.

Please feel free to comment. If you have any tips or insight on Aperture, also, feel free to share!

For more information, tips, tricks, and techniques, visit some of my other blogs.
Examples of my work are available for sale at:

1 comment: